Java求字符串数组交集、并集和差集

//求两个字符串数组的并集，利用set的元素唯一性   
    public static String[] union(String[] arr1, String[] arr2) {   
        Set<String> set = new HashSet<String>();   
        for (String str : arr1) {   
            set.add(str);   
        }   
        for (String str : arr2) {   
            set.add(str);   
        }   
        String[] result = {};   
        return set.toArray(result);   
    }   
  
    //求两个数组的交集   
    public static String[] intersect(String[] arr1, String[] arr2) {   
        Map<String, Boolean> map = new HashMap<String, Boolean>();   
        LinkedList<String> list = new LinkedList<String>();   
        for (String str : arr1) {   
            if (!map.containsKey(str)) {   
                map.put(str, Boolean.FALSE);   
            }   
        }   
        for (String str : arr2) {   
            if (map.containsKey(str)) {   
                map.put(str, Boolean.TRUE);   
            }   
        }   
  
        for (Entry<String, Boolean> e : map.entrySet()) {   
            if (e.getValue().equals(Boolean.TRUE)) {   
                list.add(e.getKey());   
            }   
        }   
  
        String[] result = {};   
        return list.toArray(result);   
    }   
  
    //求两个数组的差集   
    public static String[] minus(String[] arr1, String[] arr2) {   
        LinkedList<String> list = new LinkedList<String>();   
        LinkedList<String> history = new LinkedList<String>();   
        String[] longerArr = arr1;   
        String[] shorterArr = arr2;   
        //找出较长的数组来减较短的数组   
        if (arr1.length > arr2.length) {   
            longerArr = arr2;   
            shorterArr = arr1;   
        }   
        for (String str : longerArr) {   
            if (!list.contains(str)) {   
                list.add(str);   
            }   
        }   
        for (String str : shorterArr) {   
            if (list.contains(str)) {   
                history.add(str);   
                list.remove(str);   
            } else {   
                if (!history.contains(str)) {   
                    list.add(str);   
                }   
            }   
        }   
  
        String[] result = {};   
        return list.toArray(result);   
    }